An ability to tune the wavelength of a tunable transmitter in a transceiver from a remote site is very desirable for the following applications: 1) the mitigation of the interferometric beat noises (IBN) by avoiding the overlap of the wavelengths of two transmitters in a link where there are finite optical reflections along the link and SWSF BiDi smart transceivers are used, and 2) the link optimization of individual channel of a WDM communication system using duplex type smart transceivers or conventional two-wavelength BiDi smart transceivers.
For an optical link using SWSF BiDi transceivers in non-WDM communication systems or WDM, including conventional WDM or dense WDM (CWDM or DWDM) communication systems, the IBN generated, during optical to electrical (O/E) conversion at an optical receiver, between the optical spectral components of the intended signal from one transmitter and the optical spectral components of the unwanted, reflected signal of the other transmitter along the optical link will interfere with an intended signal and degrade signal to noise ratio (S/N) of the intended signal such that the communication optical link may not work properly, or even may be shut down; the IBN becomes biggest when the spectral components of two transmitters are overlapping on each other's. To suppress this IBN, there are two options: 1) Option #1, use of angled polished connectors (APCs) wherever physical connections with connectors are needed along the optical link to minimize the optical reflection at the connection, and 2) Option #2, use of the wavelength of one transmitter which is outside the wavelength spectra of the other transmitter in the link while allowing the reflections along the optical link. The Option #1 might be neither practical nor appealing to network owners or service providers, considering that 1) almost all the connectors of currently deployed outside plant (OSP) link fibers are polished or ultra polished type connectors (PC or UPC) where an air gap between two connectors at the connection is always possible causing 13 dB to 14 dB of optical reflection and converting all these PC or UPC connectors into APC connectors will be quite expensive, 2) owners of OSP link fibers might not be interested in replacing all the PC or UPC connectors with APC connectors to lease the OSP fibers to the customers, and 3) transceivers with APC connectors cost more than those with PC or UPC connectors. The Option #2, however, is expected to be very attractive to network owners or service providers since this approach allows finite reflections along the optical link and does not require any specific type of connectors such as APC connectors; this offers network owners or service providers, for the first time, their own choice of selection of connector type in their communication systems using SWSF BiDi transceivers while taking full advantage of all the merits of the SWSF BiDi transceivers. With this Option #2, the mitigation of the IBN can be achieved through tuning the wavelength of transmitters such that the wavelength spectra of a transmitter of the SWSF BiDi transceiver at one end of the optical link is not overlapping the wavelength spectra of a transmitter of the SWSF BiDi transceiver at the other end of the optical link. This is particularly important when there are finite optical reflections along the optical link, and the difference in received optical power level, at an optical receiver, between the intended signal and the reflected signal is less than 13 dB.
For an optical link using transceivers other than SWSF BiDi transceivers in a WDM (CWDM or DWDM) communication system which is composed of, at both ends of a link, conventional duplex type transceivers (or two-wavelength BiDi transceivers) with a specific wavelength for individual channel of the link, an optical MUX, a link optical fiber, and an optical DEMUX, it is not rare that a service provider encounters occasions of deploying a transceiver the transmitter wavelength of which, set initially by the transceiver supplier, might not be at the center or the optimum of the composite wavelength bandwidth of the optical MUX and DEMUX along each channel. This would result in the link budget very tight without much available operational system margin which must be allocated for any robust communication system, whereas the optimization of wavelength of the transmitter of the transceiver could help each channel of the WDM link with an extra operational system margin.
Certain communication systems, therefore, will benefit with a transceiver which is equipped with the adjustability of the wavelength of a transmitter in the transceiver as described above. Since 1) a communication system consists of, at least, two transceivers where the transmitter of one transceiver is transmitting a signal to the receiver of another transceiver, and 2) the optimum wavelength of each transmitter depends solely on the system in which the transceiver is operating, the controllability of the wavelength of the transmitter in one transceiver by another transceiver will be a desirable feature. This is particularly true if two transceivers are physically separated far away from each other. In other words, a remote controllability of the wavelength of a tunable transmitter of one transceiver by another transceiver will be very valuable, considering the facts that 1) the adjustment of its wavelength can be executed by the technician at the CO where all the necessary test equipments are accessible easily and 2) another technician does not have to be present simultaneously at the site of the transceiver which is in need of adjustment of its wavelength; this will save a lot of capital and operating expenditures (CAFEX and OPEX) by the service provider/operator. This necessitates a new, novel approach to achieve this remote controllability of the wavelength of a tunable transmitter in a transceiver.